Fe–Cu Alloy Nanozymes with Enhanced Oxidase-Like Activity for Multiplex Antioxidant Detection

Single-atom iron catalysts have emerged as promising mimics of oxidases; however, strategies to enhance their intrinsic catalytic activity remain underexplored. Herein, waste pitch and eggshells are utilized for fabricating high-performance nanozymes by coloading nanocopper and iron single atoms onto nitrogen-doped carbon nanotubes (Fe/Cu@NCNTs). It has been demonstrated that copper nanoparticles serve as a critical modulator, electronically tuning the iron sites, which increases the Fe2+/Fe3+ ratio and promotes the formation of Fe–Cu nanoalloys. These synergistic effects significantly enhance the oxidase-like activity of the catalyst. The optimized Fe/Cu@NCNTs exhibit a 48.7% higher specific activity and superior substrate affinity compared with the Fe@NCNTs counterpart. Leveraging this enhanced catalytic performance, a smartphone-assisted colorimetric sensing platform was developed for the rapid visual detection of multiple analytes. Furthermore, by incorporating a three-channel sensor array (TMB, ABTS, and OPD) with pattern recognition analysis, the platform accurately discriminates between nine antioxidants at concentrations as low as 10 μM. This work not only provides valuable insight into the mechanistic role of copper in enhancing the oxidase-like activity of iron single-atom catalysts but also offers a versatile and high-throughput sensing platform that advances the application of nanozymes in complex sample analysis.